The right of unlimited debate in the Senate, including the filibuster, is a key component of the Senate’s functioning. Unlimited debate has two sides: protector of political minorities from the tyranny of the majority, or a tool of partisan obstruction.

The strategy of “talking a bill to death” was common enough by the 1850s to be named the filibuster, derived from the Spanish word “filibusteros”—which described the pirates then raiding Caribbean islands.

The earliest filibusters led to demands for what we now call “cloture,” a method for ending debate and bringing a question to a vote.

Filibusters became more frequent in the late 19th and early 20th centuries. As the sheer amount of work to be done in each session has grown, a filibuster might disrupt legislation.

In 1917, senators adopted Senate Rule 22, to limit filibusters. The rule allowed the Senate to invoke cloture and limit debate with a two-thirds majority vote. Over the next four decades, the Senate managed to invoke cloture only five times.

Filibusters proved useful to southern senators who tried to block civil rights legislation, including anti-lynching bills. Not until 1964 did the Senate successfully overcome a filibuster to pass a major civil rights bill.

In 1975, the Senate reduced the number of votes required for cloture to 60 of the 100 senators. Today, filibusters remain a part of Senate practice, although only on legislation. The Senate adopted new precedents in the 2010s to allow a simple majority to end debate on nominations.

The most familiar type of filibuster is the marathon speech by a small group of senators, or even a single senator. The record for the longest individual speech goes to South Carolina's Strom Thurmond, who filibustered for 24 hours and 18 minutes against the Civil Rights Act of 1957.

Source: About Filibusters and Cloture | Historical Overview
Courtesy of U.S. Senate